(a) Field of the Invention
The invention relates to an apparatus and method for manufacturing molten irons, and more particularly, to an apparatus and method for manufacturing molten irons in which iron ores and additives are dried while being conveyed, and then by the sensible heat of exhaust gas of a fluidized-bed reactors, the iron ores and additives are charged to the fluidized-bed reactors to thereby manufacture molten irons.
(b) Description of the Related Art
The iron and steel industry is a core industry that supplies the basic materials needed in construction and in the manufacture of automobiles, ships, home appliances, and many of the other products we use. It is also an industry with one of the longest histories that has progressed together with humanity. In an iron foundry, which plays a pivotal roll in the iron and steel industry, after molten irons (i.e., pig iron in a molten state) are produced using iron ores and coals as raw materials, steel is produced from the molten irons then supplied to customers.
Approximately 60% of the world's iron production is realized using the blast furnace method developed in the 14th century. In the blast furnace method, coke produced using as raw materials iron ores and bituminous coal that have undergone a sintering process are placed in a blast furnace, and oxygen is supplied to the furnace to reduce the iron ores to iron to thereby manufacture molten irons. The blast furnace method, which is a main aspect of molten irons production, requires raw materials having a hardness of at least a predetermined level and grain size that can ensure ventilation in the furnace. Coke in which a specific raw coal that has undergone processing is needed as a carbon source used as fuel and a reducing agent. Also, sintered ore that has undergone a successive compacting process is needed as an iron source. Accordingly, in the modern blast furnace method, it is necessary to include raw material preparation and processing equipment such as coke manufacturing equipment and sintering equipment. Therefore, not only is it necessary to obtain accessory equipment in addition to the blast furnace, but equipment to prevent and minimize the generation of pollution in the accessory equipment is needed. The amount of investment, therefore, is considerable, ultimately increasing manufacturing costs.
In order to solve these problems of the blast furnace method, significant effort is being put forth in iron foundries all over the world to develop a smelting reduction process that produces molten irons by directly using fine coal as fuel and a reducing agent, and also directly using fine ores, which make up over 80% of the world's ore production, as an iron source.
The smelting reduction process typically uses a two-stage process of preliminary reduction and final reduction. The conventional molten iron manufacturing apparatus includes a fluidized-bed reactor that forms fluidized beds, and a melter-gasifier that forms coal packed bed and that is connected thereto. Iron ores and additives at room temperature are charged in the fluidized-bed reactor to undergo preliminary reduction. Since high-temperature reduced gas is supplied from the melter-gasifier to the fluidized-bed reactor, the iron ores and additives increase in temperature as a result of making contact with the high-temperature reduced gas. At the same time, 90% or more of the iron ores and additives at room temperature are reduced, and 30% or more of the same are calcined and charged to the melter-gasifier.
Coal is supplied to the melter-gasifier to form a coal packed bed, and the iron ores and additives at room temperature undergo smelting and slagging in the coal packed bed to be discharged as molten irons and slag. Oxygen is supplied through a plurality of tuyeres installed to an outer wall of the melter-gasifier such that the coal packed bed is burned and then the oxygen is converted into high temperature reduced gas, after which the high temperature reduced gas is supplied to the fluidized-bed reactor. Following reduction of the iron ores and additives at room temperature, they are exhausted outside. A temperature of the emitted exhaust gas is approximately 680° C., and a pressure thereof is 1.7˜2.5 bar.
In the case where iron ores are charged to the fluidized-bed reactor for reduction into reduced iron, in order to prevent the reduced iron from sticking to the fluidized-bed reactor and in order to prevent thermal loss in the melter-gasifier, additives such as limestone and dolomite are charged to the fluidized-bed reactor together with the iron ores. The additives are typically around 15˜20% of the total amount of the charged material.
Prior to charging the iron ores and additives to the fluidized-bed reactor, the iron ores and additives are dried in a drying apparatus to thereby ensure the free flow of these materials in the fluidized-bed reactor. To perform this operation, hot air is supplied to the drying apparatus to dry the iron ores and the additives. Since the iron ores makes up 80% or more of the combination with the additives, overall operating conditions are determined based on the requirements of the iron ore. However, because the additives have a grain size and density that are less than that of the iron ore, a significant amount of loss of the additives with a small grain size occurs if dried under the same conditions as the iron ore. Further, the drying apparatus frequently malfunctions since a substantial load is given to the same in order to realize favorable drying. Finally, 50% or more of the iron ores become fine ore of 1 mm or less to thereby clog the drying apparatus, thereby necessitating frequent production stoppages.